Denim fabrics are old and well known and are usually comprised of a firm twill-weave construction and usually are woven from 100% cotton yarns. Such fabric is characterized by having a whitish tinge which increases with wear that is obtained by using relatively white undyed filling yarns together with surface dyed or colored warp yarns and the twill construction is usually made with either a right hand or left hand twill. Standard denim fabrics are also usually blue in color which is achieved by using warp yarns that have been dyed with indigo dyes.
Indigo and the dyes resulting therefrom have been available for centuries and is a type of vat dye. While indigo dyes are normally water insoluble organic substances they can be reduced to a water soluble form and used to dye fabrics, and following dyeing the dye is oxidized which returns the dye to its water insoluble form on the yarn.
It has primarily been the use of indigo dyes and 100% cotton yarns that has given rise to the popularity of denim fabric today.
Denim fabric produced from 100% cotton yarns result in an esthetically pleasing fabric that exhibits good warp and filling tear strength. Denim fabrics that incorporate filament types of filling yarns would, of course, produce a much stronger fabric but produce whitening at the crease point under normal use because, such fabrics do not exhibit as good elbow/knee strength nor good flex abrasion strength as those that incorporate filament type filling yarns. Also, such fabrics can often exhibit too much warp or filling shrinkage. Further, the brushing of such fabrics can undesirably affect the color or shading of the fabric sometimes making the shade appear very uneven and does produce a weakening of the warp or filling yarns.
Part of these defects result from the use of standard indigo dyeing techniques. Indigo dyeing is usually carried out at room temperatures, normally from 70.degree. F. to 90.degree. F., and the dye does not usually penetrate through the whole yarn or fiber bundle notwithstanding that indigo dyeing is usually performed on wet fabrics. In fact, we have found that the wet nature of the yarn is detrimental to penetration. Accordingly, in regular indigo dyeing only the exterior layer of the yarn will have been dyed while the core of the indigo dyed yarns usually remain relatively undyed and this is referred to as ring dyeing. Thus, with wear, the shade of denim fabrics will lighten and the so called "washed" look will be achieved. It should also be pointed out that when polyester/cotton blended yarns are passed through an ordinary indigo dye bath, while the exterior portion of the cotton becomes dyed, the polyester remains undyed.
Various types of stretchable fabrics have been produced for many years and patented fabrics exemplary of such fabrics are described in the following U.S. Pat. Nos.: 246,024; 360,431; 1,601,484; 2,404,837; 3,369,281; 3,452,411; 3,486,208; 3,604,470 and 3,730,679. While these patents suggest ways to make cotton yarns stretchable, twill fabrics that exhibit warp stretch, fabrics where the stretch yarn can be included either in the warp of fill direction, improved selvages to anchor stretch yarns and stretch fabrics that can be comprised of a combination of natural and/or blended yarns none suggest the improved dyeing and finishing procedures forming part of our invention nor the resulting indigo dyed stretch denim fabrics.
Brushed, napped, scrubbed and sanded fabrics are also well known. The napping process usually involves the steps of running the cloth beneath or over a series of rollers covered with wire bristles or some abrasive surface with the rollers moving differentially with respect to cloth speed so that the rollers rub or brush against at least one side of the cloth. This brushing or napping operation raises the fibers on the surface of the cloth so that they stand up or are raised forming a nap or pile effect. In many instances, the brushing or napping process affects the filling yarns more than the warp yarns since warp yarns are usually more tightly twisted and, accordingly, it is unusual to find an indigo stretch denim fabric that has also been brushed. The brushing or napping process will, however, affect the warp yarns and it has been undesirable heretofore to nap or brush indigo dyed denim fabrics having filament filling yarns. To a degree this produces desirable results but when a filament is used as the fill yarn it would only serve to compound whitening problems which become apparent with the inclusion of the filament type of fill yarn. In fact, to limit the effects of abrasion on indigo dyed yarns, even where the use of such yarns will be in unbrushed fabrics, such yarns are frequently coated with an abrasion resistant coating, such as an acrylic, synthetic rubber or other polymeric coating, which will help prevent the wearing away of the dyed surface and the ultimate exposure of the relatively undyed core.